Stem fracture of the cementless spongy metal Lübeck hip prosthesis.

We performed 204 cementless total hip arthroplasties using a fully porous stem made of a cast cobalt-chrome-molybdenum alloy. Five stems fractured at the middle part. Champagne-fluted canals (P<.0001) and low canal fillings 1 cm below the lesser trochanter (P =.02) significantly correlated with stem fractures. Subsequent surgery revealed that all of the proximal parts were surrounded by fibrous tissue, and the distal parts showed bone ingrowth. Numerous voids were present close to the surface of the implant body. The core diameters of the fractured stems were 4 to 5 mm. The fractures may be attributed to the combination of the lack of proximal support, a champagne-fluted canal, the fully porous stem made of a cast cobalt-chrome-molybdenum alloy, and the narrow dimension of the stem core.